Falling fertility rates are a big concern for dairy farmers. You want a profitable, sustainable business. And that requires fertile cows that you can count on to maintain reliable ovulation cycles, develop viable embryos and give birth to healthy calves.
It sounds simple on paper, doesn’t it? Yet as dairy milk yields have increased over the years, dairy herd fertility rates have decreased. That challenge can be tackled through nutrition - and in this article we explain what you can do to feed your cows fertile.
Improved milk yields, decreased fertility
Up until recently, the fertility of UK dairy cows had declined for some forty years. (Just ask the University of Nottingham.) Over this time, scientists have been trying to find out why improved milk yields seemed to reduce fertility rates, with first service conception rates often falling below 40%.
Now we have some of the answers.
Back in 2002 Claire Wathes and Vicky Taylor published research in the Holstein Journal that proved the strong relationship between milk yield, fertility and conception intervals. Their studies found that a peak milk yield of about 42 kg/day seemed to be the point above which fertility became adversely affected.
During the study the cows producing less than 42 kg/day all conceived within 150 days and most took less than 100 days to get back in-calf. In contrast, only half of the higher yielding cows were back in-calf by 100 days and around a quarter took more than 150 days.
Yet high milk yields and good fertility don’t have to be mutually exclusive. You don’t always have to choose between one or the other. The secret is to get nutrition right - ensuring your herd receives the right nutrients, at the right time and in the right quantities. Simple!
The danger of negative energy balance
After calving it’s almost inevitable that your cows will enter negative energy balance (NEB). During early lactation cows cannot eat enough to meet the high energy demands of milk production. This results in a loss of body condition.
So what’s the big deal?
Faced with negative energy balance, cows’ livers produce less of an important metabolic hormone called insulin-like growth factor 1 (IGF-1). This hormone plays a key role in regulating levels of fertility and can delay the resumption of a regular oestrous cycle. Low levels of IGF-1 are associated with fewer follicles developing on the ovaries and fewer follicles being ovulated.
In short: cows in too much of a negative energy balance in early lactation can be incredibly difficult to get back in-calf. In fact if cows lose more than one BCS point in early lactation, chances of conception are significantly reduced. Fertility falls by around 10% for every 0.5 loss in BCS.
This problem is compounded by the fact that many dairy cows have been genetically selected based on their ability to mobilise body tissue to maintain high milk yields - e.g. milk off their own backs. Add in poor nutritional management and before long you are looking at losses in body condition score (BCS) across your herd. Such cows duration of negative energy balance (NEB) could last for up to 20 weeks or more after calving.
To combat this issue, it may be tempting to fatten up your cows before calving. This also has its problems. Fat cows are more likely to develop fertility problems than cows with a healthy BCS (2.5 to 3.5). These problems include cystic ovaries, metritis and increased risk of calving problems due to pelvic fatty deposits.
Make dietary changes gradually
Good nutrition can reverse fertility problems while maintaining high milk yields. But before we take a look at some specific recommendations, it’s important to remember that dairy cows must be exposed to dietary changes gradually. It takes the rumen at least two weeks to adapt to changes. Radical changes in diet can make fertility problems worse, not better.
Feed your herd fertile
On paper, using nutrition to feed your herd fertile is simple. It’s no more complex than making sure your herd’s diet meets the necessary protein, fat, energy and mineral requirements. In practice, getting it right is a little more tricky.
One for all versus one for each
All cows behave differently in the way they mobilise body reserves during lactation. It’s a complex equation based on genetics, metabolic condition and disease status. In an ideal world each cow in your dairy herd would have a diet that’s personalised to their specific metabolic requirements. Of course that’s not quite practical in real life.
Remember Wathes and Taylor from the beginning of the article? Their research revealed an interesting dichotomy. Cows in negative energy balance could enhance their fertility rates with diets that stimulated insulin. Yet while that proved to boost rates of ovulation, too much insulin was detrimental to oocyte quality.
In short by feeding diets to stimulate insulin in early lactation and lower insulin during the mating period, you can increase pregnancy rate without compromising milk yield or cow health. A simple takeout from that is to promote insulin when cows are not cycling, then lower insulin for cows that are cycling but conceiving.
AHDB Dairy recommends that for optimum fertility, cows should calve down at a BCS of 2.75-3.0 and lose no more than half a point by service. Don’t rely on making changes in body condition during the dry period.
Beware excessive protein
It takes a lot of energy to digest protein. That can exacerbate energy deficits, so it may be better to consider making up for negative energy balances with other macronutrients such as fat.
Fat is your friend. As long as you use it properly.
Pound-for-pound fat has the highest energy density of any nutrient, with around 2.5-times the energy concentration of cereals. That makes fat an incredibly efficient way to meet those enhanced energy demands. Certain fats are also known to increase progesterone – a hormone that plays an important role in facilitating healthy pregnancies.
Yet feeding fats is not without risks. Unprotected or rumen-active fats and oils decrease fibre digestion in the rumen leading to lower energy availability from the diet. That’s the opposite of what you’re trying to achieve. The answer is to supplement diets with ingredients that don’t break down in the rumen. And that’s where Megalac comes in.
Megalac is a rumen-protected fat supplement that combines natural plant oil with calcium. It’s highly digested in the acidic lower gut - with the enrgy intake going straight to where the cow needs it most. Megalac has the highest independently-measured net energy value of any feedstuff and is perfect to feed during early lactation when cows experience negative energy balance. Brand new research is also suggesting that the combination of fatty acids in Megalac influence the production of insulin in a positive way, ensuring a balanced partitioning of nutrients between milk and body fat.
It’s one of several reasons Megalac has been proven to improve fertility.
Make sure feed is freely available (and tastes nice)
It sounds obvious, but you need to make sure your feed is palatable and freely available across your farm. When you make it easy for your herd to eat, they are likely to eat more. And remember the aim to prevent fertility losses is to mitigate against negative energy balance during early lactation.
To sum up:
- Fertility is mostly influenced by events around calving and early lactation, rather than during actual service period
- Fertility loss is caused by complications associated with negative energy balance and BCS loss
- Most critical periods to maintain regular fertility are during dry period and during first few weeks of lactation
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